What Is It? #17

For a change of pace this month we're going to the light microscope (but sticking with diatoms!). These lovely little plants come from the mudflats of the Bay of Fundy, and were studied by Marsha Trites as part of her Honours Thesis in Biology. Your job is to figure out why they appear blue:

A. They turn blue when they die and become cold

B. They have been stained with a fluorescent dye to make them appear blue with illumination from a mercury light source

C. The fine details of their silica "shell" (the frustule) diffract light such that only blue light is transmitted

D. They absorb cobalt from the Fundy sediments

E. Someone has been fooling around in Photoshop